1. Field of the Invention
The invention relates to a method for supplying an internal combustion engine with conditioned gas, particularly air, preferably on test benches, including the supply of humidity and/or temperature-conditioned gas to the internal combustion engine, as well as a device to carry out this method. The invention also relates to a method for determining the quantities of pollutants in the exhaust gases of an internal combustion engine, including the determination of the pollutant concentration and the quantity of the flowing exhaust gas, whereby dilution of the exhaust gas takes place by using a diluent gas of known composition. The invention also relates to a device to carry out this additional method.
2. The Prior Art
The condition of the intake air influences the operating behavior of an internal combustion engine to a great extent. For example, the engine torque increases in gasoline engines with increasing atmospheric pressure by approximately +0.12% per hectopascal. A temperature increase of the drawn-in ambient air by 1° C. causes in the same case a loss of power of approximately −0.5%, for example. The humidity content of the intake air has only minor direct influence on engine power; however, the consequences relative to exhaust gas emission is not to be disregarded, particularly nitrogen oxide, which can be the case in gasoline engines as well as in diesel engines. A higher humidity content of the intake air makes additionally possible in gasoline engines an earlier ignition time up to the point of the knocking limit, which has to be considered during tuning operation at the engine test bench.
Since the development of internal combustion engines places requirements that are becoming continuously higher relative to the ability to reproduce and the accuracy in test results, and based on exhaust gas regulations becoming more stringent worldwide as well as the higher power density, it is therefore necessary to eliminate all influences as much as possible which effect the test results in the development of engines. Since the intake air is also part of these influences, it is necessary to condition the same to obtain comparable test conditions at the test bench.
Known systems for conditioning of the intake air for internal combustion engines are available commercially (e.g. “Combustion Air Conditioning Unit of the firm AVL-List GmbH, Graz, Austria or FEV AirCon of the firm FEV Motortechnik GmbH, Aachen, Germany). However, these systems are directly connected to the air supply system of the internal combustion engine and they must follow in this way the changes of the operating condition of the internal combustion engine and the resulting change of airflow rate, and these systems must also follow thereby directly the changes of the rate of airflow of the internal combustion engine itself.
The maximum rate of airflow in a gasoline engine is about 40 times the minimum rate of airflow. It is therefore understandable that during rapid dynamic changes of the rate of airflow in a combustion engine, known systems can follow these changes only to a limited degree and only a poor control quality of the conditions in the air is obtained during the dynamic changes in the rate of airflow. An example for a known system of this type is described in DE 40 15 818 C2.
In DE 25 36 047 A1 is described, in contrast, a pure negative pressure simulation while no steps are taken for complete conditioning of the combustion air. Furthermore, there is a box provided in the disclosed device into which enters the combustion air intended for combustion in the internal combustion engine together with the exhaust gas of the engine, and wherein they may be combined or influence one another whereby conditioning (of the air) is made almost impossible under reliable and constant conditions. The risk of mixing of combustion air with exhaust gas is very great, especially in highly dynamic operating conditions in a device such as the one disclosed in DE 25 36 047 A1, based on pressure pulsation, wide-reaching turbulence, thermal gradients etc. In addition, the combustion air is drawn into said box depending on the demands of the engine, which does almost never allow the carrying-out of constant conditioning as well.
The first object of the invention is to avoid these and other disadvantages of the traditional conditioning method and conditioning devices, and to make possible, to a great extent, reliable and constant conditioning of the combustion air even under dynamic and highly dynamic operating conditions.
An additional subject area in the field of engine-testing technology is the exhaust gas measuring technology by which there is to be determined the existing pollutant quantities from the measurable pollutant concentrations in the exhaust gas of the engine. For this calculation is necessary the quantity (mass) of the flowing exhaust gas from which the exhaust gas sample has been taken. This has to be measured either directly or it can be determined with the use of the subsequent balance of the mass flows: supplied air mass+supplied fuel mass=discharged exhaust gas mass. The supplied fuel mass can thereby be measured highly accurate and dynamically. Relative to the term “pollutant quantity”, it is to be noted that the subject matter is almost exclusively pollutant mass in the standards and guidelines for exhaust gas analysis. Sensors to determine pollutants in a gas flow measure in general the pollutant concentration, which means the quantity of pollutants—practically exclusively the pollutant mass (e.g. in milligrams)—relative to a reference quantity of gas (mass or volume under actual or under standard conditions). The measured concentration at the measuring point has to be multiplied by the corresponding flow quantity (mass flow or volume flow).
A simple system for the accurate use of the balance equation is established when either the flow of the supplied air or, especially advantageously, the flow of the discharged exhaust gas is kept constant. This occurs, for example, in the exhaust gas testing technology with the so-called CVS systems (constant volume sampling), which are standardized and which are established accurate devices for the determination of pollutant quantities in the exhaust gas. High dilution factors are generally required for the CVS systems. Extremely low pollutant concentrations are created especially in low-pollution engines as a result thereof, which can almost not be detected any longer by the analyzers. An alternative to the CVS system for the determination of pollutant quantities is now the analysis of the undiluted or comparatively minor diluted exhaust gas in combination with the direct measuring of either the incoming flow of air mass or, especially advantageous, the flow of exhaust gas mass. However, this method could not be carried out properly up to now since the sensors needed for this purpose have various inherent faults. Among other things, the high dynamic of engine operation and the strong flow pulsation as well as the pressure pulsations overriding the average flow are detected only insufficiently and the sensors are, in general, not sufficiently suited for the hot and corrosive exhaust gases. For the solution of these problems were proposed suppression chambers and flow-measuring arrangements for the average flow, which have to be built, however, having very large dimensions, which are very difficult to be used on the engine and which oftentimes falsify the conditioned operating conditions of the engine.
It was therefore another object of the invention to provide a method and a device which make possible a precisely defined dilution of the exhaust gas and thus a precise determination of the quantities of pollutants in a simple and reliable manner.